In order to store or transfer a semiconductor wafer of 300 mm in diameter at the time of manufacturing a semiconductor, for example, a side door integrated wafer receiving jig is used which is called a front opening unified pod (FOUP) having an opening door in a front portion through which the semiconductor wafer is inserted into or taken out of the jig. The FOUP is constructed of a shell which is a holding part for receiving the semiconductor wafer and a door which is a part for opening or closing the shell. The FOUP holds the semiconductor wafer in a hermetically enclosed space to protect the semiconductor wafer from foreign matters or chemical pollution in the atmosphere.
In this respect, one of the FOUPs is, for example, an F300 wafer carrier made by Fluoroware, Inc. and its size and structure have been disclosed in detail (see, for example, Japanese Patent Application Laid-open No. 11-91864, SEMI Standard E57, E1.9, E47.1).
By the way, usually, the FOUP is molded of plastics and the hermeticity between the shell and the door is kept by a packing made of rubber or the like. However, the plastics has a property of allowing moisture and the like to pass and outside air easily intrudes through a sealing part made of the packing into the FOUP due to molecular diffusion or the like. Hence, the humidity and oxygen concentration in the FOUP tends to increase with the lapse of time.
Moreover, in a case where the semiconductor wafer having a resist deposited thereon is stored in the FOUP, an organic solvent evaporated from the resist is deposited on the inner wall of the shell. Hence, even after the semiconductor wafer having the resist deposited thereon is removed, the resist deposited on the inner wall of the shell is again evaporated to pollute the atmosphere in the FOUP. Moisture, oxygen, and organic pollutant in the FOUP grow a natural oxide film on the semiconductor wafer and cause the poor dielectric strength of an insulating film.
In this respect, for example, in a hermetically enclosed container which is one of hermetically enclosed wafer receiving jigs, there has been studied a method of solving the above problem in which a gas purge mechanism is provided to introduce an inert gas, for example, a nitrogen gas or dry air into the hermetically enclosed container to replace the atmosphere in the hermetically enclosed container with the inert gas.
There have been proposed, for example, a method of purging air in the cover of a container through a purging hole formed in a wall and discharging air in a gap between the cover and a specific base through a purging exhaust pipe (see, for example, Japanese Patent Application Laid-open No. 6-334019) and a method of discharging oxygen and moisture existing in a space formed between the cover of the hermetically enclosed container and the ascending/descending table of a hoisting and lowering unit through a through hole, an opening/closing unit, and a discharge passage to the outside of the main body of the station (see, for example, Japanese Patent Application Laid-open No. 9-246354).